The present invention claims the benefit of Korean Patent Application No. P2000-83099 filed in Korea on Dec. 27, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a display device, and more particularly, to an electroluminescence device and a method for manufacturing the same.
2. Discussion of the Related Art
Ultra thin flat panel display devices, especially liquid crystal display (LCD) devices, are widely used in monitors for notebook computers, spacecrafts, and aircrafts.
Of such LCDs, a passive luminescence LCD device includes a back light provided at the rear of a liquid crystal panel and used as a light source. The back light adds additional weight, power consumption, and thickness to the LCD device. In this respect, it is expected that the back light will eventually be replaced by an advanced high efficiency self-luminescence display device. Currently, a thin and light electroluminescence device is being researched and developed.
Electroluminescence devices can be divided into light-emitting diodes (LEDs) and electroluminescence diodes (ELDs) depending on the application principles. A LED is based on radiant transition course of electron-hole recombinations near a P-N junction. Recently, rapid development of LEDs using an organic material is in progress.
An ELD is based on luminescence generated when high energy electrons generated within a light-emitting layer excite a phosphor layer by impact. Basically, the electrons within the light-emitting layer obtain energy under a high electric field, thereby generating hot electrons. The hot electrons then excite and release an activator, thereby generating light.
ELDs are generally manufactured by a thick film printing process by using a mixture of resin and light-emitting powder. Alternatively, a thin film printing process may be used. Also, ELDs are divided into an AC type and a DC type depending on different driving modes.
A related art electroluminescence device will now be described with reference to the accompanying drawings.
FIG. 1 is a schematic view of a related art electroluminescence device. As shown in FIG. 1, the related art electroluminescence device includes a substrate 11, a transparent electrode layer 13 formed on the substrate 11 in a predetermined pattern such as a stripe pattern, a lower insulating layer 15 of SiOx, SiNx, or BaTiO3 formed on the transparent electrode layer 13, a light-emitting layer 17 of ZnS based light-emitting material formed on the lower insulating layer 15, and an upper insulating layer 19 of SiOx, SiNx, or Al2O3 formed on the light-emitting layer 17. It further includes a metal electrode layer 21 of a metal, such as Al, formed on the upper insulating layer 19, and a surface passivation layer 23 formed on the metal electrode layer 21.
In the aforementioned related art electroluminescence device, when an AC voltage is applied to the transparent electrode layer 13 and the metal electrode layer 21, a high electric field of xcx9c106V/cm is formed within the light-emitting layer 17. Electrons generated in the interface between the upper insulating layer 19 and the light-emitting layer 17 are tunneled into the light-emitting layer 17.
The tunneled electrons are accelerated by the high electric field within the light-emitting layer 17. The accelerated electrons come into collision, with an activator (Cu or Mn) within the light-emitting layer 17 so that electrons are excited from the ground state. When the excited electrons are again transited to the ground state, a unique light equivalent to the energy difference is emitted. At this time, the color of the emitted light depends on the energy difference.
A method for manufacturing the aforementioned related art electroluminescence device will now be described. As shown in FIG. 1, the transparent electrode layer 13 is formed on the glass substrate 11. In more detail, an indium tin oxide (ITO) thin film having a high conductivity and transparent physical characteristic is deposited on the substrate 11. The ITO thin film is then patterned by a photolithography process to form a stripe shape, thereby forming transparent electrodes.
Afterwards, the BaTiO3 based lower insulating layer 15 is formed on the transparent electrode layer 13 by a RF reactive sputtering process. The light-emitting layer 17 is then formed on the lower insulating layer 15.
The light-emitting layer 17 may be formed by an electron-beam deposition, e.g., by cold pressing a powder in which Cu or Mn is doped on ZnS and generating small grains. Alternatively, the light-emitting layer 17 may be formed by a sputtering method using a target.
The upper insulating layer 19 of SiOx, SiNx, or Al2O3 is formed on the light-emitting layer 17 by a sputtering process or chemical vapor deposition (CVD) process.
The metal electrode layer 21 is formed on the upper insulating layer 19. An Al or Ag thin film is formed on the upper insulating layer 19 by a thermal deposition method and then stripe shaped metal electrodes are formed to cross the transparent electrodes of the transparent electrode layer 13. The surface passivation layer 23 is finally formed on the metal electrode layer 21. Thus, the related art process for manufacturing an electroluminescence device is completed.
However, the related art electroluminescence device and the method for manufacturing the same have several problems. Since the electroluminescence device requires a high electric field, an insulating layer is required both above and below the light-emitting layer to prevent a short circuit resulting from any defect. The insulating layer limits the maximum current flowing to the device to a range corresponding to the discharge and charge displacement of the insulating layer.
In case where the light-emitting layer is formed by either a vacuum deposition method according to the sputtering method or a thick film printing method using a powder, the insulating layer is normally formed by screen printing using an organic binder. This increases the required process steps and the manufacturing cost.
Furthermore, since the insulating layer is respectively formed above and below the light-emitting layer, a voltage drop occurs as a result. For this reason, a threshold voltage required to drive the device becomes higher. In other words, an undesirably high driving voltage is required.
Accordingly, the present invention is directed to an electroluminescence device and a method for manufacturing the same that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an electroluminescence device and a method for manufacturing the same that minimize the process steps and the manufacturing cost.
Another object of the present invention is to provide an electroluminescence device and a method for fabricating the same that can obtain a sufficiently high light-emitting effect under a low driving voltage.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, an electroluminescence device according to the present invention includes a substrate, a lower electrode layer formed on the substrate, a light-emitting layer formed directly on the lower electrode layer, an upper electrode layer formed on the light-emitting layer, and a passivation layer formed on the upper electrode layer.
In another aspect of the present invention, an electroluminescence device including a substrate; a transparent electrode layer on the substrate; a light-emitting layer including a light-emitting powder formed on the transparent electrode layer, the light-emitting powder being coated with an insulating material on a surface; a metal electrode layer formed on the light-emitting layer; and a passivation layer formed on the metal electrode layer.
To further achieve these and other advantages and in accordance with the purpose of the present invention, a method for manufacturing an electroluminescence device according to the present invention includes the steps of forming a lower electrode layer on a substrate, forming a light-emitting layer directly on the lower electrode layer, forming an upper electrode layer on the light-emitting layer, and forming a passivation layer on the upper electrode layer.
In another aspect of the present invention, a method for manufacturing an electroluminescence device including the steps of forming a transparent electrode layer on a substrate; forming a light-emitting layer including a light-emitting powder on the transparent electrode layer, the light-emitting powder being coated with an insulating material with a high dielectric constant on a surface; forming a metal electrode layer on the light-emitting layer; and forming a passivation layer on the metal electrode layer.
In an exemplary embodiment of the present invention, an insulating material having a high dielectric constant is coated on a surface of a light-emitting powder without forming a separate insulating layer on and below the light-emitting layer, so that the process steps and the manufacturing cost can be minimized. Since a separate insulating layer is not formed on and below the light-emitting layer, a threshold voltage required to drive the device is not unnecessarily increased, thereby reducing the driving voltage.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.